inferior thermochemically, but have a wider liquid range. A popular bipropellant combination is A50 (50% hydrazine, 50% UDMH) These cannot be used as monoprop, because they poison the catalyst Hydrazine evolves NH3, and smells like it. Its vapors damage the eyes and the pulmonary tract. The liquid if pure, is fairly inert, but vapors form flammable mixtures in air for vapor pressures corresponding toT>40 C. the liquid decomposes exothermically if catalyzed by iron oxide, copper oxide or oxides of Pb, Mn, Mb, Ag, Hg or Cr. It is not sensitive to friction or impact Materials compatibility is an important consideration, especially for long term torage and for parts of thrusters with long life exposed to it Materials which are oK are aluminum stainless 304 or 347, titanium tantalum rhenium and platinum. also glass, Teflon and polyethylene plastics. to be avoided are copper cobalt, iron, lead, magnesium, manganese, molibdenum, mild steel, high Mo stainless(416, 303), most plastics(except as noted), wood, rags, paper. See table handed out Oils are oK for lubrication, but not if there is a catalytic bed, since it gets poisoned by the oil. Hydrazine is expensive($ 50-60/Ib for MMH, as of 1994) (2) Thermochemistry. When catalyzed either by an oxide or by a hot platinum surface, N2H4 decomposes. Since at low temperatures ammonia, NH3 is stable, the preferred end products would be NH3 +N2 3NH H3+N2 (a) However, this is a very exothermic reaction and the equilibration T would be 1650K at which temperature NH3 is not stable anymore. Hence, the final equilibrium composition would contain very little NH3, due to H3→N2+3H2 and would be at intermediate t since the latter reaction is endothermic. In practice reaction(a) is very fast(less than 1 msec) if catalyzed, while(b)is slow Hence for small decomposition chambers and high flow rates when the residence time Pas Van/m is short, reaction(b)proceeds only partially, the extent being controllable by the design conditions. The final composition and overal reaction assuming a fraction x of NH3 decomposes is N2H4→=NH3+N2 Form (1)+X(2); x=fraction of NH, that decomposes H3→5N2+2H2 NH4→(1-x)NH2+(1+2x)N2+2xH2 16. 522, Space Propulsion Lecture 5 Prof. Manuel martinez-Sanchez Page 6 of 1216.522, Space Propulsion Lecture 5 Prof. Manuel Martinez-Sanchez Page 6 of 12 inferior thermochemically, but have a wider liquid range. A popular bipropellant combination is A50 (50% hydrazine, 50% UDMH). These cannot be used as monoprops, because they poison the catalyst. Hydrazine evolves NH3, and smells like it. Its vapors damage the eyes and the pulmonary tract. The liquid, if pure, is fairly inert, but vapors form flammable mixtures in air for vapor pressures corresponding to T > 40 CD . The liquid decomposes exothermically if catalyzed by iron oxide, copper oxide, or oxides of Pb, Mn, Mb, Ag, Hg or Cr. It is not sensitive to friction or impact. Materials compatibility is an important consideration, especially for long term storage and for parts of thrusters with long life exposed to it. Materials which are OK are aluminum, stainless 304 or 347, titanium, tantalum, rhenium and platinum. Also glass, Teflon and polyethylene plastics. To be avoided are copper, cobalt, iron, lead, magnesium, manganese, molibdenum, mild steel, high Mo stainless (416, 303), most plastics (except as noted), wood, rags, paper. See table handed out. Oils are OK for lubrication, but not if there is a catalytic bed, since it gets poisoned by the oil. Hydrazine is expensive ($ 50-60/lb for MMH, as of 1994). (2) Thermochemistry. When catalyzed either by an oxide or by a hot platinum surface, N2H4 decomposes. Since at low temperatures ammonia, NH3, is stable, the preferred end products would be NH3 +N2: 3N H 4NH N 24 3 2 → + (a) However, this is a very exothermic reaction, and the equilibration T would be 1650 K, D at which temperature NH3 is not stable anymore. Hence, the final equilibrium composition would contain very little NH3, due to 2NH N +3H 3 22 → (b) and would be at intermediate T, since the latter reaction is endothermic. In practice reaction (a) is very fast (less than 1 msec) if catalyzed, while (b) is slow. Hence, for small decomposition chambers and high flow rates, when the residence time ρgas ch V mi is short, reaction (b) proceeds only partially, the extent being controllable by the design conditions. The final composition and overall reaction assuming a fraction x of NH3 decomposes is 24 3 2 3 3 22 4 1 N H NH + N (1) 3 3 Form (1)+ x(2) ; x = fraction of NH that decomposes 4 2 NH N + 2H (2) 3 3  →   →   24 3 2 2 ( ) ( ) 4 1 N H 1 - x NH + 1+ 2x N + 2xH 3 3 →